Specimen Collection

Sample stability:

• 7 days at 15-25 ^o C
• 3 weeks at 2-8 ^o C
• 8 months at -20 ^o C

4.5 mL PST Blood (Preferred)

0.5 mL Paediatric Micro-PST Blood (Preferred)

5 mL Heparin Blood

4 mL Plain Blood

3.5 mL SST Blood

0.5 mL Microsample Blood

0.5 mL Paediatric Micro-heparin Blood
Reference Intervals

Units: mmol/L

Age: Day 1 to 3	1.80 - 2.80
Day 4 to 1yr	2.10 - 2.80
>1yr:	2.10 - 2.55

This test measures total plasma calcium (includes ionised, protein-bound, and complexed fractions).

Reference ranges above apply to total calcium when serum albumin is normal , and to corrected calcium (adjusted for albumin concentration).

Serum albumin should always be measured in conjunction with total calcium, to enable calculation of corrected calcium.

Prolonged stasis during venepuncture and haemolysis will give falsely high values.

Conversion factors:

mg/100 mL x 0.25 = mmol/L

mmol/L x 4 = mg/100 mL

Uncertainty of Measurement: 5%

Turnaround Time: Within 3 hours
Assay Method

Principle : Colorimetric

Reagents: Roche CA2 kit

Analyser: Cobas c702

Diagnostic Use and Interpretation

Increased calcium concentrations: primary and tertiary hyperparathyroidism, malignancies (both with and without bone involvement), sarcoidosis, vitamin D overdosage, dehydration, Paget's disease (with immobilisation) and genetic disorders of the calcium sensing receptor.

Decreased calcium concentrations: hypoparathyroidism, pseudohypoparathyroidism, chronic renal failure, renal tubular disorders, magnesium deficiency, vitamin D deficiency, prolonged anticonvulsant therapy, acute pancreatitis, rickets and osteomalacia.

Corrected or adjusted calcium

The routine test for plasma calcium concentration measures the total calcium (bound plus ionised calcium ). Approximately 50% of plasma calcium is bound to albumin, and this bound fraction is biologically inactive. Therefore changes in albumin concentration will affect the total calcium concentration without affecting the ionised (active) fraction of plasma calcium.

In order to allow the use of a single reference interval for total calcium, irrespective of albumin concentration, the total calcium can be adjusted using a formula. This is known as the "corrected" or "adjusted" calcium.

The formula used is:

[Ca adjusted] = [Ca total] + 0.012 x (39.9 - [albumin])

Reference

James M, Zhang J, Lyon A, Hemmelgarn B. Derivation and internal validation of an equation for albumin-adjusted calcium. BMC Clinical Pathology 2008;8:12.

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427

Last updated at 15:26:00 06/01/2025